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Old June 18th, 2017, 10:19 PM   #1
Dakotap92
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Sequence?

I have a basic understanding of plc and ladder logic, motor control, inputs (pressure temp level) but I have a small project I would like to do at work. I have been looking at The click plc series from automation direct if that means anything... ok so here is the sequence. This is a water plant with two filters we would like to be able to make the filters auto backwash at a certain time during off peak hours.. ok so say 930 pm first filter backwashes after that sequence 2nd filter then backwashes then done til next day at 930pm
Here is the events that need to happen.
1. Effluent valve open to drain filter down to certain level(ultrasonic)
2.effluent valve close-drain valve open-air wash valve open-airwash blower on
3.airblower run for 10minutes
4. Airblower off -air wash valve off-backwash valve open to 10%-backwash pump on
5. Slowly open backwash valve to 100% run for 8 minutes
6.backwash valve close-backwash pump off-drain valve off
7.filter#2 start sequence
How difficult will this be is there something else that could do this job?
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Old June 18th, 2017, 10:34 PM   #2
GaryS
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Sounds like a good starter project the Click should be a good choice for this one.
the one think I would add is manual controls for everything
start each back flush manually also each valve and motor it makes trouble shooting a lot easier down the road
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Old June 18th, 2017, 10:41 PM   #3
Dakotap92
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It's all done currently with manual switches right now. Thanks for the encouragement. I really enjoy this kinda stuff. I have done all kinds of control wiring and vfd installs etc., but this would be my first hands on plc experience. I have watched a ton of videos but I just wanted to get on the forum and talk to the people that can help. There's no time rush or anything so I can take my time. I guess this would use a drum in ladder logic?
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Old June 18th, 2017, 10:46 PM   #4
OkiePC
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I have not used the Drum instruction in a Click myself, but it looks like it might be the right tool for this job.

Looks like you will want the event based triggers since some of your steps are finished based on an event and not strictly a time.

I have used sequencer type instructions with other PLCs so some general advice:

Use more steps than you think you need. You can always "peg" duplicate output patterns in sequential steps that might be useful later when you find out some enhancement to the operation. If there are spares to work with already in existence, you will save time when you must edit the sequence and the addresses will already be reserved. Your steps 4 and 6 looks like candidates for this. In step 6, you might find out you need to start closing the backwash valve for a few seconds before you shut off the pump, or vice versa to, for example, avoid a pressure spike in the backwash line or jamming a motor operated valve.

Document it well. If you can produce a spreadsheet or other type of document for folks that may need to troubleshoot the process, that will be invaluable to them.

Plan for all the potential pitfalls and where reasonable, include steps to deal with them:
What happens if the filter level never drops to the required level in step 1 (say the sensor has slime on it and it holding its last good value)?

Make use of the HMI if available to display the step number and required conditions for completion.
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It's not all the variables I am most concerned with, it's the undiscovered constants.
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Old June 18th, 2017, 10:53 PM   #5
Dakotap92
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Thanks for the reply! Good question . I wondered how to put safety measures in. All of our valves have confirmed open and close switches to drive a indicator light or whatever you want. I guess really to do this safely it would need to confirm valves are opened or closed to follow through the next event. Last thing I want is a hung up valve to flood the place.
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Old June 18th, 2017, 11:00 PM   #6
GaryS
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I hate to be different OKie but I would not user a Drum instruction for this
it's been my experience that most newbie's find it difficult to follow a drum instruction and you really don't have that many steps to deal with I see only 5 or 6 and all have a different trigger for each this makes it difficult to implement and follow
you have level, time valve position all triggering the steps
don't forget the feedback from all the valves and pumps that you need to tack
and what about fault conditions
a list of things to think about, take your time and think your way through it one step at a time.
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Old June 18th, 2017, 11:09 PM   #7
Dakotap92
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I'm gunna see if I can find a video of the process so you guys can see what I'm trying to do might make the picture easier.
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Old June 18th, 2017, 11:10 PM   #8
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Even though I'm sure this is child's play for you pros lol
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Old June 19th, 2017, 04:36 AM   #9
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Whenever i do a filter controller, I write or or ask for a Bingo chart. This is basically a table with each step as a numbered row, and each valve, motor etc as a column. For each step you mark whether each valve or motor is on or off. I like to increment in steps of 10 to allow for future additions when the engineer realizes he's forgotten something.

Once the sequence is running, i monitor if the step counter remains static for too long on a step (i.e. stuck waiting for a condition). Different preset depending on the step. If it does i reset to a safe state and raise an alarm for the operator.

Which is something you maybe need to think about. If this is now happening off peak with presumably no one around, how will someone know if something goes wrong? If you do not have a monitoring or telemetry system you might want to investigate even a simple SMS alarm dialer to notify operators of faults
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Old June 19th, 2017, 08:17 AM   #10
Dakotap92
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We have a auto dialer that could be used for that. There's a second plant that runs 24/7 so it could call that plant. But that sounds exactly like what we need to do.. or even being able to backwash from other plant? You guys are a heap of help . I will work on a excel sheet . Think about safety measures. Get a plc with the appropriate accessories. And report back. If in the mean time any moment has any more suggestions please let me know.
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